The SNAP Instrument Suite Session Chris Bebek (for Mike Lampton) Lawrence Berkeley National Laboratory 9 January 2003

2Outline What drives the instrument implementation concept —Requirements —Constraints What does the instrument implementation concept look like How is the instrument operated

3 How Science-Driven Requirements map onto Instrument Concept Instrument A large FOV (0.7 sq. deg. ). Observation cadence commensurate with SNe evolution (every 4 days). Allocation of time for photometry and follow up spectroscopy (60/40). Imager Wavelength coverage from 400 nm to 1700 nm. Use two plate scales to cover the wavelength range to obtain time efficient photometry. 9 filters. Required S/N(epoch) versus magnitude achieved with appropriate duration and number of exposures. Zodiacal light - limited measurements Spectrograph Wavelength coverage from 350 nm to 1700 nm. S/N = 20 Resolution ~100 (  ) Measurement Program ~50 Type Ia SNe per 0.03 in z from z=0.3 to 1.7 (2500 total). Follow-up spectroscopy near peak luminosity.

4 How Science-Driven Requirements map onto Instrument Concept Measurement Program Photometry R.F. U, B, V, (R)-band light curves. R.F. B-band measurement to 2% at peak. K-correction R.F. B–V color evolution. Malmquist bias. Rise time. Peak to tail luminosity ratio. Spectroscopy UV metalicity features – strength and location. S and Si features —SII 5350Å line,  w = 200Å —SII “W” shape,  w = 75Å —SiII 6150Å line,  w= 200Å Ejecta velocity,  15Å Calibration Instrument Imager Wavelength coverage from 400 nm to 1700 nm. Use two plate scales to cover the wavelength range to obtain time efficient photometry. 9 filters. Required S/N(epoch) versus magnitude achieved with appropriate duration and number of exposures. Zodiacal light - limited measurements Spectrograph Wavelength coverage from 350 nm to 1700 nm. S/N = 20 Resolution ~100 (  )

5 Photometry illustration Wavelength Flux U B V R Color: K correction Photo z Classification

6 Science-driven requirements on the Instrument Concept Measurement Program Photometry Spectroscopy UV metalicity features – strength and location. S and Si features —SII 5350Å line,  w = 200Å —SII “W” shape,  w = 75Å —SiII 6150Å line,  w= 200Å Ejecta velocity,  15Å Host galaxy z. Instrument Imager Spectrograph Wavelength coverage from 350 nm to 1700 nm. S/N = 20 Resolution ~100 (  )

7 Spectroscopy illustration SII “W” SiII Metallicity

8 Space operation impacts on the Instrument Concept Reliability Avoid moving parts —No coolers —No gimbaled solar panels —No filter wheel —Allow a shutter Avoid multiple focal planes —Eliminate multiple adjuster sets —Coalesce visible, NIR, and spectrograph into one focal plane Satellite Body mounted radiator and solar panels provide a stable platform for long exposures, Passive, radiative cooling, Folded TMA telescope, But, quantizes satellite orientation relative to Sun and hence orientation of the focal plane relative to observation fields.

9 Other inputs into the Instrument Concept Cosmic rays Proton rate is ~4 /s/cm 2, after shielding. CCD impact is about 1% of pixels are contaminated per 100 s of exposure time. Long integrations need to be broken into a sequence of short exposures (say 300 s for photometry and 1000 s for spectroscopy). Dithering This is a procedure to increase photometric accuracy in undersampled images. Also necessary to average out sub-pixel size response variations. Long integrations need to be broken in several exposures with well known spatial offsets.

10Telescope Three-mirror Anastigmat: Annular field maximizes sky coverage Wide flat field available All-reflector design, no refractors Folded for compactness Convenient focal surface location for passive cooling Manufactured and operated warm SNAP Requirements Aperture approx 2.0 meters Field of view 1.4 sq degree Diffraction limited longward of 1.0 um Span wavelengths 0.35 to >1.7 um Flat focal surface with > 100um/arcsec Stray light << Zodiacal Design Features: Lightweight mirrors of ULE or Zerodur Structure of CFRP with low CTE Tripod secondary support structure Rigid aft structure for folding mirror, tertiary, and detector support MIrrors & structure run at 290K

11 Instrument working concept Shutter Particle/ Thermal/ Light shield CCDs/ HgCdTe Thermal links Spectrograph Cables/ FE elec Near electronics Radiator Guiders Cold plate Filters

12 Focal plane - imager Coalesce all sensors at one focal plane. —36 2k x 2k HgCdTe NIR sensors covering μm. —36 3.5k x 3.5k CCDs covering μm. —4 1k x 1k star guider CCDs. —Two channel spectrograph on the back with access port on the front. Common 140K operating temperature. Guide off the focal plane during exposures. r in =6.0 mrad; r out =13.0 mrad r in = mm; r out = mm CCDs Guider HgCdTe Spectr. port Spectrograph

13 Focal plane - imager Fixed filter mosaic on top of the imager sensors. —3 NIR bandpass filter types. —6 visible bandpass filter types. Note the symmetry – a star can be swept l-r, r-l, t-b, or b-t and still be measured in all filters. More on this later.

14 Focal plane - spectrograph Spectr. port Integral field unit based on an imager slicer. Input aperture is 3” x 6” – reduces pointing accuracy req. Simultaneous SNe and host galaxy spectra. Internal beam split to visible and NIR. Separate prism disperser and detector for each leg. Input port Slicer Prism BK7 Prism CaF 2 NIR detector Vis Detector Spectrograph SlicerPupil mirrors

15 Step the focal plane through the observation field. N steps in each CCD filter; 2N steps in each HgCdTe filter (N will be 4). Fixed length exposures determined by a shutter (T exp will be 300 s). The multiple exposures per filter are used —to implement dithering/drizzle; —to eliminate cosmic ray pollution. NIR filters have twice the area of visible filters; this combined with time dilation will achieve the desired S/N in CCDs and HgCdTe. All stars see all filters (modulo scan field edge effects). Fields revisited with fixed cadence. SNe evolution can be followed for 100’s of days. Obs. Concept - repetitive program Actual dithering would be at the sub or near pixel level. Note the longer integrated exposure time in the larger filters.

16 Why 2D Symmetric Toy satellite demo. Solar cells must be kept within 90 o of Sun. Radiator must be kept pointing to dark space.

17 Why 2D Symmetric

18 Why 2D Symmetric During each 4-day period, the survey filed is scanned.

19 Why 2D Symmetric

20 Why 2D Symmetric Must rotate the satellite 90 o relative to survey field every 3 months.

21 Why 2D Symmetric

22 Why 2D Symmetric Note the scan is now along an orthogonal satellite axis to the prior scan.

23 Why 2D Symmetric

24 Obs. Concept – targeted program SNe candidates are scheduled for spectrographic measurement near peak luminosity. Light curve and color analysis done on ground to identify Type Ia and roughly determine z. Note peak luminosity is 14 days to 40 days after discovery for z = 0.3 and 1.7 respectively. Star is steered into spectrograph port.

25 What needs to be done First and foremost is the development of detectors CCDs - pursuing LBNL technology —Enhanced radiation tolerance —Good spatial response commensurate with small pixel size —Extended QE in the red NIR —Have been relying on WFC3 funding for developing of 1.7 μm material —Exploring multiple vendors —Establishing characterization sites within the collaboration

26 Imager Sensors Specs VisibleNIRUnits FOV0.34 deg 2 Plate scale (nominal) asec Wavelength nm 8060% Read noise (multiple reads) 45e Dark current e/s/pixel Filters (1+z spaced B-band) 63 Read time time.20 s

27 Spectrograph Sensors Specs VisibleNIRUnits Wavelength coverage nm Plate scale0.15 asec Spatial resolution0.15 asec Field-of-View3 x 6 asec 2 Resolution100  8060% Read Noise25e- Dark Current e-/s/pixel With these specs, total integration time (w/ 1000 s exposures) is